Press machines for pressing between a pair of dies while decreasing and increasing the distance between the dies have been used.
As a method for determining whether press working is acceptable or not, a method for determining whether press working is acceptable or not based on a comparison with a load curve of an intended quality, for example, has been proposed (Patent Document 1).
Specifically, methods have been disclosed according to which a reference waveform for a pressed product of an intended quality is registered in advance, and whether press working is acceptable or not is determined based on a comparison between the reference waveform and a load waveform during press working (Patent Documents 2 and 3).